Acetic acid is commonly found in food ingredients, and it can be used as an antiseptic. Measuring concentration of acetic acid could be done by simply using colored label. As acetic acid detection in food ingredients proliferates, developing toxic-free labels is now a necessity. This research reported the result of an experiment on developing green labels for detecting acetic acid. The green label is made from the extract of chitosan and purple sweet potatoes as smart materials. The extraction color of the purple sweet potatoes changes from red to purple for pH buffer condition from 2 to 7. Chitosan solution and the extract then undergo a casting process in order to make a label, resulting in a transparent thin bright yellow plastic label. The concentration of the detected acetic acid solutions in the experiment was varied from 0% to 15%. The evidences from the experiment showed that the label changed its color from bright yellow to dark yellow in accordance to the changed of acetic acid concentration, which was increasing gradually. By using UV-Vis spectrometer, characterization for the label color change before and after detecting acetic acid was done. By the result, the green label made from extract of chitosan and purple sweet potatoes can be used effectively for detecting acetic acid as simply and quickly.